This invention relates to precision gear reduction units, and more particularly to gear reduction units having very low backlash.
It is known that the control of the extent of backlash within a required range may be accomplished by holding the gear dimension and the center distance tolerances to extremely close limits. In a gear reduction unit the free play between the gears at the input stage is less critical than at the output or second stage, by reason of the gear reduction factor. Many designs have been proposed in the past to remove backlash from gear trains, including arrangements for loading the gears, such as by using split gears and the like. However, these arrangements tend to increase the torque or power requirements to drive the gear reduction unit. Where very low drive torques are available, it has been necessary to make high precision gears and then match the gear selectively, or to position one gear along an inclined or canted shaft to remove the backlash. Also, backlash eliminating arrangements have been suggested as shown in the U.S. Pat. of Barber, No. 2,382,846 issued Aug. 14, 1945, in which each end of the shaft supporting a planatary gear is mounted for rotation within an eccentric bushing, thus requiring two eccentrics to be adjusted to remove the backlash.